The present invention relates to an apparatus including internally-meshing (or hypocyclic eccentric) planetary reduction gear to serve as a rotary driving apparatus and, more specifically, to such a rotary driving apparatus further including a free-wheel mechanism.
A mechanism for driving the wheels of an industrial vehicle is known, in which the output rotational speed of a hydraulic or electric motor is reduced by an internally-meshing planetary reduction gear, and then transmitted to the axle of the vehicle, whereupon the wheels are rotated.
In such a rotary driving mechanism for an industrial vehicle or the like, the following problem arises when some trouble has occurred in the motor and, accordingly, the vehicle has to be moved to another place for repair work; it is difficult to move the vehicle because of the constrained behavior of the mechanism for rotating the wheels. That is, as the vehicle is being moved, the speed of rotation of the wheels is increased by the internally-meshing planetary reduction gear, and transmitted to the motor. Thus, the torque needed to rotate the wheels is amplified while making the rotation of the wheels difficult.
With a view to overcoming the above problem, a driving mechanism which further includes a free-wheel mechanism has been proposed (for example, in Japanese Utility Model Unexamined Publication No. 62-161026).
The apparatus disclosed in the above-identified publication, that is, a known rotary driving apparatus with an internally-meshing planetary reduction gear that has a free-wheel mechanism, will be described with reference to FIGS. 6 and 7.
The rotation of a hydraulic or electric motor 1 is transmitted to a pinion 3 provided on an end portion of an input shaft 2 so that three driving gears 4 are rotated by the pinion 3. The driving gears 4 rotate eccentric body shafts 5 on which two sets of eccentric bodies 6 are serially provided. As a result, external gears 7, each having a trochoidal or circular-arc tooth shape and each being provided on one of the sets of the eccentric bodies 6, are caused to orbit (i.e., effecting only orbital motion without rotating on its own axis). The external gears 7 mesh with an internal gear 9 having internal teeth consisting of pins 8 so that the internal gear 9 rotates at a reduced speed. Thus, a wheel 10 of the vehicle, which is integrated with the internal gear 9, is caused to rotate.
Suppose some trouble has occurred in the motor 1 and the vehicle has to be moved in order to perform repairs. When the vehicle is being towed for this purpose, the wheel 10 rotates with difficulty because the internally-meshing planetary reduction gear constituting the rotation transmitting mechanism acts as a speed-increasing mechanism. Even if the resistance to the rotation of the motor 1 is small, the resistance is amplified, making it difficult for the motor 1 to be rotated from the side of the wheel 10.
The known mechanism has an arrangement in which the pinion 3 is axially movable. When trouble has occurred in the motor 1, the pinion 3 is axially moved so that it is released from its engagement with the driving gears 4.
However, the known rotary driving device including the free-wheeling mechanism has the following drawback. That is, even when the pinion 3 is axially moved and released from its engagement with the driving gears 4, the rotation of the wheel 10 causes the rotation of the internal gear 9, the external gears 7, the eccentric body shafts 5 and the driving gears 4, thereby involving resistance caused by the rotation of these component parts. Therefore, when this resistance is great, it is still difficult to move the vehicle. In particular, rotation is transmitted from the internal gear 9 to the external gears 7 under great resistance. Thus, it is impossible to move the vehicle using a small towing force.
Another drawback of the known rotary driving apparatus with the free-wheel mechanism is that the state of engagement between the pinion 3 and the driving wheels 4 cannot be checked. As a result, when an operation is to be performed, the operator cannot be positively informed of whether this engagement is established or interrupted. Thus, the operability of known apparatus is not very good.